The only handgun cartridge that really lives down to its reputation is .25 ACP, also known as 6.35mm Browning.
Dating to the dawn of the last century and designed for little blowback vest pocket autos, even the warmest Euro loadings are decidedly tepid. While SAAMI maximum pressure for the cartridge is 25,000 PSI, which is similar to the .22LR's 24,000 PSI, it tends to use heavier bullets that travel at a lower velocity.
At Marion County Fish & Game, I chronographed some Fiocchi 50gr FMJ ammo out of my Titan .25, using the
Garmin Xero C1 Pro. The ten shot string averaged 752 feet per second, which is a feeble 63 foot-pounds of muzzle energy, if that's a number that's important to you.
For comparison, .22LR Federal Punch flirts with supersonic velocities out of even a pocket pistol, averaging 1,108fps from the Ruger LCP II .22 the last time I chronoed a batch. (That's 79 foot pounds of energy, for what it's worth.)
.25ACP, even the Euro-spec ball, is known for minimal penetration, and if you're using a hollow point projectile that, by some miracle, expands despite the low velocity, you're going to lose what marginal penetration you do have. If, for some reason, all you have is a .25, load it with Fiocchi or S&B or similar FMJ and aim with care.
.
